Introduction to antibiotics and their classification

• A 76 year old patient is admitted to the hospital with likely severe community-acquired pneumonia. What antibiotics should be started?

  Coamoxiclav and clarithromycin
• What is an antibiotic?

  Naturally-occurring agent produced by a microbe that inhibits or kills another.

  (Usually means any anti-bacterial agent, synthetic, semi-synthetic or naturally-occurring)
• What is an antimicrobial agent?

  Any drug that inhibits or kills, a bacterium, virus, fungus

  Includes anti-bacterial, anti-fungal and anti-viral
• Why do we prescribe antimicrobials?

  To prevent infection (prophylaxis)

  To treat suspected infection
• What are 2 types of antibiotic prophylaxis ?

  1. Surgical prophylaxis (clean-implant, contaminated surgical procedures)

  2. Medical prophylaxis (chemotherapy, transplant immunosuppression, post splenectomy)
• What is an empiric therapy?

  Antibiotic treatment before specific culture results reported or confirmed
• What is targeted therapy?

  Treatment focused to known pathogen and its susceptibility
• What are the 4 ways to classify antibiotics?

  Antibiotic family

  Mechanism of action

  Spectrum: broad or narrow

  Activity: bactericidal or bacteriostatic
• What are the classes of antibiotic families?

  Beta-lactams

  Glycopeptides

  Aminoglycosides

  Quinolones

  Macrolide

  Tetracyclines
• What are the mechanisms of action of antibiotics?

  Cell wall synthesis

  DNA replication

  RNA synthesis

  Protein synthesis

  Antimetabolites
• What are the typed of antibiotic spectrums?

  Broad and narrow
• Is Piperacillin-tazobactam narrow or broad spectrum?

  Broad
• What is piperacillin-tazobactam effective against?

  Some gram positive cocci, gram negative bacilli including pseudomonas species and anaerobic bacteria
• What are the pros of broad spectrum antibiotics?

  Polymicrobial / unknown aetiology
• What are the cons of broad spectrum antibiotics?

  Superinfection
• What are some examples of superinfection?

  C. difficile, candida spp
• Is penicillin G broad or narrow spectrum?

  Narrow
• What is penicillin G active against?

  Gram positive cocci and gram negative bacilli
• What are the pros of narrow spectrum antibiotics?

  Minimal disruption of normal flora
• What are the cons of narrow spectrum antibiotics?

  Not suitable for empiric therapy of many infections
• What are different antimicrobial activities?

  Bacteriostatic prevent bacteria multiplying

  Bactericidal antibiotics kill the bacteria
• What antimicrobial activity does penicillin have?

  bactericidal
• What antimicrobial activity does tetracycline have?

  Bacteristatic
• What is the difference between bacteriostatic and bactericidal?

  Bacteriostatic inhibits growth of susceptible bacteria rather than killing them immediately

  Bactericidal kills susceptible bacteria
• True or false? Bacteriostatic will result in bacterial death?

  True, eventually with immune defences
• Bactericidal antibiotics are important to used if?

  Immunodeficient or for certain difficult infections
• What does susceptibility testing predict?

  Predict in vivo patient response via an in-vitro test
• What does susceptibility test aid in?

  Bacterial identification
• What does susceptibility provide?

  Epidemiological data to support empiric therapy and guideline development
• What does susceptibility testing define?

  Organism as susceptible, intermediate or resistant
• What are 3 methods of antimicrobial susceptibility testing?

  Disk diffusion

  Minimum inhibitory concentration (MIC), usually now automated

  Genotypic methods
• What is disk diffusion?

  Disk with defined amounts of different antibiotics are placenta on an agar plate inoculated with a bacterial suspension. Antibiotics disuse out of disc into agar.
• What does the zone around an antibiotic disk that has no growth refer to?

  Zone of inhibition
• What is a zone of inhibition measured in? compared to?

  mm and compared to a standard interpretation chart to categorise the isolate (susceptible, intermediate, resistant)
• What does the zone see reflect?

  Susceptibility or resistant
• Can the minimum inhibitory concentration (MIC) be determined from the disk diffusion test?

  No
• What type of test is a disk diffusion ?

  Qualitative test
• What are the pros of disk diffusion?

  Easy and cheap

  May test 4-6 agents at one time
• What is a minimum inhibitory concentration (MIC)?

  The lowest concentration of an antibiotic required to inhibit the growth of bacteria
• What do the concentrations chosen for testing reflect?

  Tissue concentration